Electronic endoscope system and light source for endoscope

ABSTRACT

An electronic endoscope system, including: a light source that emits light having a visible light wavelength region; an optical filter that has transmission peaks at least at two particular wavelengths in a continuous wavelength region including the visible light wavelength region and has a transmissivity higher than zero and lower than a half of each transmission peak between the transmission peaks of the at least two particular wavelengths, the optical filter having a transmissivity of zero at a wavelength region other than an interval between the transmission peaks of the at least two particular wavelengths; a solid-state image pick-up device that receives reflected light from an object which is irradiated with illumination light via the optical filter; and an image generation unit configured to generate a color image to be displayed on a monitor by processing an image signal outputted by the solid-state image pick-up device.

BACKGROUND OF THE INVENTION

The present invention relates to an electronic endoscope system and alight source for an endoscope for observing a color image of an object,and particularly to an electronic endoscope system and a light sourcefor an endoscope suitably configured to allow an operator to observe aparticular biological structure.

As a system for making a diagnosis on a body cavity of a patient, anelectronic endoscope system is known and in practical use. Among suchelectronic endoscope systems, there is an electronic endoscope systemconfigured to illuminate an object through a narrow band filter lettinglight with a certain wavelength band for which a particular biologicalstructure shows a high degree of absorption pass therethrough, and togenerate a spectral image highlighting the particular biologicalstructure by receiving a scattered component of the light from theobject, so that tissue information of the biological structure can bevisualized.

In Japanese Patent Publication No. 3583731 (hereafter, referred to aspatent document 1), an example of an endoscope apparatus for making anobservation by narrow-band light is described. In the endoscopeapparatus described in patent document 1, a narrow band filterconfigured to narrow a bandwidth of at least one of wavelength regionsof illumination light is arranged on an optical path proceeding from anillumination light supply unit to an image pick-up unit and a band imageof an object having a discrete spectral distribution obtained by thenarrow-band light is generated. By using the endoscope apparatus of thistype, it becomes possible to visually recognize tissue information of aparticular biological structure of the object in a manner in which thetissue information is layered. As a result, tissue information at adesired depth in a tissue surface of the biological structure can beobtained.

SUMMARY OF THE INVENTION

However, in the endoscope apparatus described in patent document 1,information cannot be obtained in a wavelength band other than atransmitted main wavelength because the illumination light has thediscrete spectral distribution. Therefore, there is a possibility thattissue information of the object is partially lost. Furthermore, since atransmission range of the illumination light is limited by the narrowband filter, the amount of light is decreased and thereby the brightnessof the obtained image decreases.

The present invention is made in consideration of the above describedcircumstances. The present invention is advantageous in that it providesan electronic endoscope system and a light source for an endoscopeconfigured, when a particular biological structure is observed withnarrow-band light, to prevent loss of information concerning aparticular biological structure and to enhance the brightness andcontrast of an image.

According to an aspect of the invention, there is provided an electronicendoscope system, which includes: a light source that emits light havinga visible light wavelength region; an optical filter that hastransmission peaks at least at two particular wavelengths in acontinuous wavelength region including the visible light wavelengthregion and has a transmissivity higher than zero and lower than a halfof each transmission peak between the transmission peaks of the at leasttwo particular wavelengths; a solid-state image pick-up device thatreceives reflected light from an object which is irradiated withillumination light via the optical filter; and an image generation unitconfigured to generate a color image to be displayed on a monitor byprocessing an image signal outputted by the solid-state image pick-updevice. The optical filter has a transmissivity of zero at a wavelengthregion other than an interval between the transmission peaks of the atleast two particular wavelengths.

When an object is illuminated via the above described optical filter, aspectral image of which brightness and contrast are enhanced can begenerated and displayed on a monitor. Furthermore, since information ona wavelength region between the transmission peaks of the particularwavelengths can be obtained, occurrence of lack of information can beprevented. That is, it becomes possible to enhance brightness andcontrast while preventing of occurrence of lack of information when aparticular biological structure is observed through use of narrow bandlight.

The at least two particular wavelengths may include a wavelength regionof around 420 nm at which hemoglobin has a larger absorptive property.With this configuration, it becomes possible to observe vesselstructures near a surface layer and in a deep layer.

The electronic endoscope system may further include: an optical filterswitching unit configured to cause the optical filter to be insertedinto or retracted from an illumination optical path of the light source;and an operation unit configured to receive a user operation. Theoptical filter switching unit may cause the optical filter to beinserted into or retracted from the illumination optical path inaccordance with the user operation received through the operation unit.By thus retracting the optical filter from the illumination optical pathas the need arises, it becomes possible to display a normal color imageon the monitor.

According to another aspect of the invention, there is provided a lightsource for an endoscope, which includes: a light source that emits lighthaving a visible light wavelength region; and an optical filter that hastransmission peaks at least at two particular wavelengths in acontinuous wavelength region including the visible light wavelengthregion and has a transmissivity higher than zero and lower than a halfof each transmission peak between the transmission peaks of the at leasttwo particular wavelengths. The optical filter has a transmissivity ofzero at a wavelength region other than an interval between thetransmission peaks of the at least two particular wavelengths.

With this configuration, it becomes possible to enhance brightness andcontrast while preventing of occurrence of lack of information when aparticular biological structure is observed through use of narrow bandlight.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is illustrates an outer appearance of an electronic endoscopesystem according to an embodiment of the invention.

FIG. 2 is a block diagram illustrating a configuration of the electronicendoscope system according to the embodiment.

FIG. 3 is a graph illustrating a spectral property of an optical filterprovided in a processor according to the embodiment.

FIG. 4A illustrates an observation image obtained when an object isilluminated without using the optical filer, and FIG. 4B illustrates anobservation image obtained when the object is illuminated via theoptical filter.

FIG. 5 shows a spectral property of an optical filter provided in aprocessor according to another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment according to the invention is described withreference to the accompanying drawings.

FIG. 1 illustrates an outer appearance of an electronic endoscope system1 according to the embodiment. As shown in FIG. 1, the electronicendoscope system 1 has an electronic scope 100 for imaging an object.The electronic scope 100 includes a flexible tube 11 covered with asheath 11 a having flexibility. To a tip of the flexible tube 11, a tippart unit 12 externally covered with a resin housing having rigidity iscoupled. A bending part 14 arranged between the flexible tube 11 and thetip part unit 12 is configured to freely bend through remote controlfrom a forehand operation unit 13 (e.g., a rotating operation to abending operation knob 13 a) attached to a proximal end of the flexibletube 11. This bending mechanism has a known configuration installed in ageneral electronic scope, and is configured to bend the bending part 14by drawing an operation wire provided in the flexible tube 11 inconjunction with a rotational operation to the bending operation knob 13a. By changing the direction of the tip part unit 12 through the abovedescribed bending operation, an imaging area of the electronic scope 100can be moved.

As shown in FIG. 1, the electronic endoscope system 1 has a processor200. The processor 200 is integrally provided with a signal processingdevice which processes signals from the electronic scope 100, and alight source which illuminates, through the electronic scope 100, a bodycavity to which natural light does not reach. In another embodiment, thesignal processing device and the light source may be provided asseparate devices.

The processor 200 is provided with a connector part 20 corresponding toa connector part 10 provided at the proximal end of the electronic scope100. The connector part 20 has a structure corresponding to a structureof the connector part 10, and is configured to connect the processor 200with the electronic scope 100 electrically and optically.

FIG. 2 is a block diagram illustrating a configuration of the electronicendoscope system 1. As shown in FIG. 2, the electronic endoscope system1 has a monitor 300 connected to the processor 200 via a cable. Itshould be noted that in FIG. 1 the monitor 300 is omitted for the sakeof simplicity.

As shown in FIG. 2, the processor 200 has a system controller 202 and atiming controller 204. The system controller 202 controls variouscomponents constituting the electronic endoscope system 1. The timingcontroller 204 outputs clock pulses for adjusting signal processingtimings to various circuits in the electronic endoscope system 1.

After activation by a lamp power igniter 206, a lamp 208 emits lighthaving a spectral property expanding from a visible light region to aninfrared region, i.e., an invisible light region (or light including atleast a visible light region). As the lamp 208, a high luminance lamp,such as a xenon lamp, a halogen lamp or a metal halide lamp, issuitable. The illumination light emitted from the lamp 208 is condensedby a condensing lens 210 and is limited via an aperture stop 212 to havea suitable light amount.

To the aperture stop 212, a motor 214 is mechanically coupled via atransmission mechanism, such as an arm and a gear, not shown. The motor214 is, for example, a DC motor, and is driven under control of a driver216. The aperture stop 212 is activated by the motor 214 to change theaperture size thereof. In order to adjust the brightness of an imagedisplayed on the monitor 300 to have a suitable brightness, the aperturestop 212 limits the light amount of the light emitted from the lamp 208depending on the aperture size thereof. A reference value regarding asuitable brightness of an image can be set or changed in response to anadjusting operation for luminance by an operator through a front panel218. Since a photochromatic circuit which adjusts luminance bycontrolling the driver 216 is a known circuit, explanation thereof isomitted.

Various types of forms can be considered as the configuration of thefront panel 218. Examples of a specific configuration of the front panel218 include hardware keys provided for the respective functions mountedon a front surface of the processor 200, a touch panel GUI (GraphicalUser Interface) and a combination of hardware keys and a GUI.

The illumination light which has passed through the aperture stop 212 isspectrally divided by an optical filter 213, and is incident on anentrance end face of a LCB (Light Carrying Bundle) 102. To the opticalfilter 213, a motor 215 driven under control of the driver 216 ismechanically coupled via a transmission mechanism, such as an arm and agear, not shown. The motor 215 drives the optical filter 213 so that theoptical filter 213 is inserted into or retracted from an optical path inresponse to a switching operation to the front panel 218 by theoperator. While the optical filter 213 is at a retracted position fromthe optical path, the illumination light which passed the aperture stop212 directly enters the entrance end face of the LCB 102. As the motor215, a galvano motor or a servo motor can be considered.

The illumination light which has entered the entrance end face of theLCB 102 propagates through the LCB 102 while repeating total reflection.The illumination light which has propagated the LCB 102 emerges from anexit end face of the LCB 102 arranged at the tip of the electronic scope100. The illumination light emerging from the exit end face of the LCB102 illuminates the object via a light distribution lens 104. Thereflected light from the object is converged by an objective lens 106 toform an optical image on pixels of a light-receiving surface of asolid-state image pick-up device 108.

The solid-state image pick-up device 108 is, for example, a single-chipcolor CCD (Charge Coupled Device) imaging sensor, and is configured toaccumulate charges responsive to the light amount of the optical imageformed on the pixels of the light-receiving surface and to convert thecharges into an image signal corresponding to R, G and B. After beingamplified by a pre-amplifier not shown, the converted image signal isoutputted to a signal processing circuit 220 via a driver signalprocessing circuit 112. In another embodiment, the solid-state imagepick-up device 108 may be a CMOS (Complementary Metal OxideSemiconductor) imaging sensor.

The driver signal processing circuit 112 accesses a memory 114 to readout unique information of the electronic scope 100. The uniqueinformation of the electronic scope 100 includes, for example, thenumber of pixels, sensitivity, a supported rate and a model number ofthe solid-state image pick-up device 108. The driver signal processingcircuit 112 outputs the unique information read from the memory 114, tothe system controller 202.

Based on the unique information of the electronic scope 100, the systemcontroller 202 executes various calculations and generates controlsignals. Using the generated control signals, the system controller 202controls the operation and timing of various circuits in the processor200 so that processes suitable for an electronic scope being connectedto the processor 200 can be achieved. The system controller 202 may havea table in which a model number and control information suitable for theelectronic scope of the model number are associated. In such a case, thesystem controller 202 refers to the control information in the table,and controls the operation and timing of the various circuits in theprocessor 200 so that processes suitable for an electronic scope beingconnected to the processor 200 can be performed.

In accordance with the timing control by the system controller 202, thetiming controller 204 supplies clock pulses to the driver signalprocessing circuit 112. In accordance with the clock pulses suppliedfrom the timing controller 204, the driver signal processing circuit 112drives and controls the solid-state image pick-up device 108 at timingsynchronizing with a frame rate of images processed by the processor 200side.

To the signal processing circuit 220, the image signal is inputted fromthe driver signal processing circuit 112. The mage signal is subjectedto various processes including a clamping process, a knee process,γ-process, an interpolation process, AGC (Auto Gain Control) and A-Dconversion, and thereafter is buffered into frame memories respectivelycorresponding to R, G and B, at a frame rate. Each buffered color signalis swept out at timing controlled by the timing controller 204, and isconverted into a video signal based on a predetermined standard, such asan NTSC (National Television System Committee) or a PAL (PhaseAlternating Line). By sequentially inputting the converted video signalinto the monitor 300, an image of the object is displayed on the monitor300. While the object is illuminated by inserting the optical filter 213into the optical path, a spectral image highlighting a particularbiological tissue (e.g., blood vessels are separated in a layerstructure (a blood vessel in a surface layer and a blood vessel in adeep layer are displayed in different colors)) is generated anddisplayed. While the object is illuminated in a state where the opticalfilter 213 is retracted from the optical path, a normal color image isgenerated and displayed. When a spectral image is generated, a colorconversion process which is different from that for a normal color imageis performed.

FIG. 3 is a graph illustrating a spectral property of the optical filter213. In FIG. 3, the vertical axis represents a normalizedtransmissivity, and a horizontal axis represents a wavelength (unit:nm). As shown in FIG. 3, the spectral property of the optical filter 213has transmission peaks around 420 nm, 550 nm and 650 nm, respectively,and has a transmissivity higher than or equal to a certain value betweenthe transmission peaks.

The transmissivity defined between the transmission peaks is higher thanzero and lower than a half of the each transmission peaks. In thisembodiment, by intentionally setting the transmissivity for light otherthan the particular wavelength for highlighting the particularbiological tissue to be higher than zero, the light amount cut by theoptical filter 213 is suppressed and the brightness of the spectralimage is enhanced. Furthermore, since information regarding regionsbetween the transmission peaks can also be obtained, occurrence of lackof information can be prevented. Furthermore, by setting thetransmissivity to be lower than a half of each transmission peak,deterioration of detection sensitivity with respect to the particularbiological tissue can be suppressed effectively. It is more preferablethat the lower limit of the transmissivity between the transmissionpeaks is higher than or equal to 5% of each transmission peak, and theupper limit of the transmissivity between the transmission peaks islower than or equal to 10% of each transmission peak. By thus settingthe transmissivity, it becomes possible to obtain an image having a highdegree of contrast while maintaining a certain degree of brightness.

Furthermore, in the optical filter 213 according to the embodiment,transmissivity of a wavelength region other than the intervals betweenthe transmission peaks is zero. As a result, it becomes possible toeliminate an undesirable red component in comparison with the case wherethe transmissivity higher than the certain value is maintained over theentire region from the visible light region to the infrared light region(e.g., 380 nm to 1000 nm). Consequently, an image having a higher degreeof contrast can be obtained. That is, according to the embodiment, it ispossible to generate a spectral image having a higher degree ofbrightness and contrast, and display such an image on the monitor 300,by illuminating an object via the optical filter 213. It is alsopossible to prevent occurrence of lack of information.

FIG. 4A illustrates an observation image obtained when an object isilluminated without using the optical filer 213. FIG. 4B illustrates anobservation image obtained when the object is illuminated via theoptical filter 213. The images in FIGS. 4A and 4B are obtained byshooting the same object (a buccal cavity). As shown in FIG. 4A, whenthe optical filter 213 is not used, a mucous membrane structure in abuccal cavity is observed as a brighter image. Since the particularbiological structure is not highlighted, the image is totallyrepresented as a smooth expressionless image in FIG. 4A. On the otherhand, when the optical filter 213 is used, the particular biologicalstructure is highlighted, and the mucous membrane structure in thebuccal cavity can be observed in a single image together with theparticular biological structure as shown in FIG. 4B. The wavelength bandaround 420 nm or 550 nm corresponding to the transmission peak is anabsorption band for hemoglobin. Specifically, the wavelength around 420nm is more absorptive to hemoglobin than the wavelength around 550 nm.Therefore, the particular biological structure observed in this case isblood vessels in the buccal cavity. Even when the illumination light isprovided via the optical filter 213, the illumination light is notnarrow band light but has a certain degree of broadness. Such aconfiguration makes it possible to prevent occurrence of lack ofinformation, and to observe various types of biological structurescorresponding to respective invasion depths of wavelengths. As a result,diagnostic performance can be enhanced.

The foregoing is explanation about the embodiment. It is noted that thepresent invention is not limited to the above described configuration,and can be varied within the scope of the invention. For example, thespectral property of the optical filter 213 is not limited to that showin FIG. 3, and may be set depending on the type of a biologicalstructure to be observed. As another example of a spectral property,FIG. 5 shows a spectral property of an optical filter 213′. In FIG. 5,the vertical axis represents a normalized transmissivity, and thehorizontal axis represents the wavelength (unit: nm). As shown in FIG.5, the spectral property of the optical filter 213′ has transmissionpeaks around 420 nm and 550 nm, and has a transmissivity higher than orequal to a certain value between the transmission peaks. As in the caseof FIG. 3, the transmissivity higher than or equal to the certain valuebetween the transmission peaks is higher than or equal to zero and islower than a half of the transmission peaks, and is preferably 5% to 10%of the transmission peak. In contrast to the optical filter 213 shown inFIG. 3 having the transmission peaks at the three wavelength bands sothat a natural color image is obtained, the optical filter 213′ shown inFIG. 5 has transmission peaks at two wavelength bands so as to be ableto obtain an image having a high contrast.

This application claims priority of Japanese Patent Application No.P2012-180902, filed on Aug. 17, 2012. The entire subject matter of theapplication is incorporated herein by reference.

What is claimed is:
 1. An electronic endoscope system, comprising: alight source that emits light having a visible light wavelength region;an optical filter that has transmission peaks at least at two particularwavelengths in a continuous wavelength region including the visiblelight wavelength region and has a transmissivity higher than zero andlower than a half of each transmission peak between the transmissionpeaks of the at least two particular wavelengths, the optical filterhaving a transmissivity of zero at a wavelength region other than aninterval between the transmission peaks of the at least two particularwavelengths; a solid-state image pick-up device that receives reflectedlight from an object which is irradiated with illumination light via theoptical filter; and an image generation unit configured to generate acolor image to be displayed on a monitor by processing an image signaloutputted by the solid-state image pick-up device.
 2. The electronicendoscope system according to claim 1, wherein the at least twoparticular wavelengths include a wavelength region of around 420 nm atwhich hemoglobin has a larger absorptive property.
 3. The electronicendoscope system according to claim 1, further comprising: an opticalfilter switching unit configured to cause the optical filter to beinserted into or retracted from an illumination optical path of thelight source; and an operation unit configured to receive a useroperation, wherein the optical filter switching unit causes the opticalfilter to be inserted into or retracted from the illumination opticalpath in accordance with the user operation received through theoperation unit.
 4. A light source for an endoscope, comprising: a lightsource that emits light having a visible light wavelength region; and anoptical filter that has transmission peaks at least at two particularwavelengths in a continuous wavelength region including the visiblelight wavelength region and has a transmissivity higher than zero andlower than a half of each transmission peak between the transmissionpeaks of the at least two particular wavelengths, the optical filterhaving a transmissivity of zero at a wavelength region other than aninterval between the transmission peaks of the at least two particularwavelengths.